The use of compositions able to indicate, by changing their color, the loss of efficiency of a consumer article with which the compositions are associated, is quite wide. The usefulness of such compositions is quite apparent, as they allow the visual assessment of the right moment at which the consumer article needs to be renewed.
The known compositions are used in consumer articles such as air fresheners (e.g. see S. C. Johnson, EP 0309173 A2), packaging films (e.g. see University of Akron, U.S. Pat. No. 5,501,945) or coating films (e.g. see Nippon Photograph Printing, JP 03199964).
In general, changes occurring in a consumer article during its use or storage, induce the compositions to respond, and therefore to change color, indicating the loss of efficiency. The most commonly occurring variations include pH, redox potential, solvent, pressure or light irradiation changes.
European application EP 309173 A2 discloses the use of a homogeneous indicator composition that includes a volatilizable non-aqueous solvent, a soluble polar indicator dye and a soluble proton donating compound. During the evaporation of the volatilizable non-aqueous solvent, the concentration of the proton donating compound progressively increases, thus inducing a gradual pH change, the latter producing a gradual color change indicating the lost of efficiency. A limitation of such a composition comes from the fact that the preferred proton donors are liquid and therefore must be less volatile than the solvent in order to ensure the functioning of the composition. A further serious drawback of such a composition comes from the fact that the color change, and therefore the information provided to the consumer concerning the efficiency of the article, occurs only gradually and is spread out through the useful life of the article. This gradual change makes it difficult to assess when the article has effectively become inefficient in use.
The Japanese document JP 03199964 discloses a printable coating film for discoloration in the course of time, formed by an ink containing a powder of (hydro)oxides, a dye, a solvent that has at least one oxygen atom in its formula and a resin for the binder as essential components. In said film, the evaporation of the solvent induces the color change.
In order to achieve a good matching between the rate of evaporation of the solvent and the effective life of the associated article, the realization of an efficient film is complex and requires a very careful dosing of the quantity of solvent and of the thickness of the film. Furthermore, as above, the main weakness consists in the fact that the color change is a gradual one, as clearly stated by the authors.
Despite prior known compositions aimed at indicating when consumer articles have become inefficient in use, there is still a need for compositions which are of simple preparation and able to provide an unambiguous indication of the consumer article status through a clear and unambiguous color change.